Cambridge Grammar of English Hardback with cd-rom a comprehensive Guide

TYPES OF MEANING

379

There are two main types of modal meaning. 

One meaning is to do with certainty, probability and possibility, with an

assessment of potential facts and with deductions or predictions based on 

the assessment:

I 

might see you later.

(it is possible, not certain)

---

I

’ll see you tomorrow.

(speaker is certain)

The other meaning involves getting things done or trying to control the course of

events. Modals used in this way express degrees of obligation and whether or not

something is necessary, desirable, permitted or forbidden. This use also refers to

volition, people’s will to do or not do things, and to their ability to do things:

You 

may go now.

(speaker grants permission)

I 

must be careful what I say.

(speaker expresses necessity/obligation)

Liz 

can work right through the night without getting tired.

(speaker refers to ability)

Often, the same modal form can be used with different meanings, depending on

context:

I don’t know. You 

may be right.

(possibility: It is possible you are right.)

[spoken instruction to students taking a timed examination]

You 

may start now.

(permission: You are allowed to start now.)

Could it be the other one that’s causing the problem?

(possibility: Is it possible that the other one is causing the problem?)

Could we come and see it on Saturday?

(permission: request for permission to come)